Hitherto, planar display panels of the type that a plurality of linear electrodes are arrayed in a matrix pattern in opposed relation with a dischargeable gas medium therebetween, and a voltage is applied to selected ones of the electrodes on both sides to develop gas discharge at the intersects of the both-side electrodes, have been disclosed in, e.g., Japanese Unexamined Patent Publication No. 3-160488 and No. 2-90192 and Japanese Unexamined Utility Model Publication No. 3-94751.
Those conventional planar display panels are constructed such that two insulating substrates each being light-transparent are bonded to each other to define a space, electrodes are provided on each of the substrates to form matrix-like discharge electrodes in the space and to position in opposed relation with the space between the electrodes on both sides, and partitions are provided to define a discharge space for each of the electrodes. Then, display control is performed by selecting desired ones of the matrix-like electrodes disposed in opposed relation. It has been therefore impossible to perform display control independently for each of display cells. Also, the above-mentioned structure has necessarily resulted in a large thickness of the planar display panel.
Another conventional planar panel utilizing gas discharge to effect display is described in Ohwaki and Yoshida, "Plasma Display", November 1983.
This panel is constructed by arranging comb-like electrodes coated with an insulating material, e.g., glass, such that the comb-like electrodes are opposed to each other in a matrix pattern with a discharge space between the electrodes on both sides. Display cells arrayed in units of a row or column are driven together by one comb-like electrode.
Display control of the panel is performed by three operations; i.e., a writing operation in which, of the comb-like electrodes in a row-and-column pattern, the comb-like electrodes on the scan side are driven successively while minute discharge is produced in a display cell locating between the selected comb-like electrode and the electrode opposed to it in the matrix pattern, a sustaining operation for selectively causing only those display cells, in which minute discharge is produced by the writing operation, to emit light over an entire display screen, and a total-writing/total-erasing operation for bringing the display cells into the same electrical condition over the entire display screen.
To display an image, it is required to control luminance for each of the display cells. Because each control and display electrode deals with many display cells at a time and the display cell operates with a binary characteristic (taking only two states of emitting light or not), a special method must be used to achieve gradation display. One driving method is disclosed in, e.g., Japanese Unexamined Patent Publication No. 6-186927.
According to the disclosed driving method, gradation display is achieved by dividing a display period into a plurality of periods having different sustaining periods (or different levels of luminance in sustaining periods) for the purpose of luminance representation, and performing operations of writing and sustaining display data in the respective divided periods, thereby combining the luminance levels in the divided periods with each other.
With the above conventional panel driving method, however, because the opposing matrix electrodes are used for control of display discharge, each electrode must control 100 ore more display cells at a time. Then, display is effected by time sequentially performing a writing step of driving scan electrodes in a group of matrix electrodes one by one, a sustaining step of alternately applying a sustaining voltage pulse to the group of matrix electrodes so that only those display cells, into which display data has been written, emit light for display, and a total-discharging/total-erasing step for making even electrical conditions of the cells effecting display and the cells not effecting display, respectively.
Further, in such a sequence control, the control process necessarily depends on characteristics of the display cells which are susceptible to large individual differences during the manufacturing steps, such as a voltage value to start discharge of each display cell, a minimum voltage value to sustain the discharge, and a writing voltage value for producing writing discharge. The voltage for sustaining the discharge, in particular, often has an allowable range of as narrow as 10 to 20 V because upper and lower limit values of the voltage are determined respectively by the discharge starting voltage and the minimum sustaining voltage.
For the above reasons, control margins for ensuring stable display cannot be set to large values, and the display sustaining voltage, the writing voltage, the discharge starting voltage, etc. need to be adjusted for each display panel. If those voltage values are fluctuated with the continued operation, they must be adjusted again. Another problem is that complicated characteristics of the display cells are subject to large fluctuations even in one sheet of display panel, and hence a production yield is reduced.
Further, in the above-described gradation control method for the conventional gas discharge panel, at least two operations of writing data and sustaining display need to be performed in the number of combinations enough to achieve gradation representation, and the writing operation takes at least 1 to 2 msec. Accordingly, the display sustaining period is discontinuous with the writing periods interleaved therein.
For the gradation representation, control is performed to finish in one sequence (about 16 ms: frame frequency 60 Hz). However, because luminance control cannot be performed continuously in point of time within one sequence, there occurs a mismatch between the gradation representation of display (gradation representation resulted from driving the panel as per design) and perception of luminance change by the human eyes. This raises a problem that discontinuous points in gradation, i.e., the so-called pseudo-contour, is perceived and quality of image display is greatly deteriorated.
The present invention has been accomplished in view of the state of art set forth above, and its object is to provide a planar display panel in which display cells of a display panel can be driven individually on the cell-by-cell basis, and a discharge space has a structure capable of reducing a thickness of the planar display panel, as well as a method for manufacturing the planar display panel.
Another object is to provide a controller for a planar display panel, with which switching control is performed for each of individual electrodes provided independently of one another in one-to-one relation to display cells of a planar display panel, in which the display cells can be individually driven on the cell-by-cell basis, thereby achieving gradation control.
Still another object is to provide a method for driving a planar display panel, which can perform control of sustaining discharge for a display panel having an electrode structure and a panel structure, which enable display cells to be driven individually on the cell-by-cell basis, regardless of discharge characteristics of the individual display cells, particularly a difference between a discharge starting voltage and a minimum discharge sustaining voltage, thereby providing a sufficiently large margin for discharge control, and which inserts an operation for stabilizing discharge at intervals of a predetermined period, thereby sustaining more stable discharge.
Still another object is to provide a method for driving a planar display panel, which performs discharge control in a continuous time range within one sequence, enabling display luminance to be represented in one continuous period, and hence can achieve gradation display suitable for image display.